docs: def bandpass(self, frequency, q=1.0):
          """bandpass takes 2 parameters: filter center frequency in Hz and "q"
          or band-width (default=1.0).
  
          It gradually removes frequencies outside the band specified.
          """
          self.command.append('bandpass')
          self.command.append(frequency)
          self.command.append(str(q) + 'q')
          return self